Detergents used for washing tableware (i.e., glassware, china, silverware, plastic, etc.) or kitchenware in the home or institution have long been known. Dishwashing in the seventies is reviewed by Mizuno in Vol. 5, Part III of the Surfactant Science Series, Ed. W. G. Cutler and R. C. Davis, Marcel Dekker, N.Y., 1973, incorporated by reference. The particular requirements of cleansing tableware and leaving it in a sanitary, essentially stainless, residue-free state has indeed resulted in so many particular compositions that the body of art pertaining thereto is now recognized as quite distinct from other cleansing product art. Additionally, the body of art pertaining to fabric cleaning is immense and encompasses many formulations designed for stain removal, many including bleaches.
However, consumers continue to experience problems with stain removal on various substrates, including typical kitchenware surfaces. In particular, formulators have experienced difficulties in formulating detergents which remove both hydrophobic and hydrophilic stains. Typically for stain removal, formulators have turned to chlorine bleach or sources of hydrogen peroxide and bleach activators.
Numerous substances have been disclosed in the art as effective bleach activators. One widely-used bleach activator is tetraacetyl ethylene diamine (TAED). TAED provides effective hydrophilic cleaning especially on beverage stains, but has limited performance on hydrophobic stains, dingy stains and body soils. Another type of activator, such as nonanoyloxybenzenesulfonate (NOBS) and other activators which generally comprise long chain alkyl moieties, is hydrophobic in nature and provides excellent performance on dingy stains and carotenoid stains.
It would seem that a combination of bleach activators, such as TAED and NOBS, would provide an effective detergent composition which would perform well on both hydrophilic and hydrophobic soils and stains. However, many of the hydrophilic activators developed thus far, including TAED, have been found to have limited efficacy, especially at laundry liquor temperatures below 60.degree. C. Another consideration in the development of consumer products effective on both types of soils is the additional costs associated with the inclusion of two or more bleach activators. Accordingly, it is of substantial interest to the manufacturers of bleaching systems to find a less expensive type of bleaching activator.
Chlorine bleaches are effective for stain andlor soil removal. While chlorine bleach is a very effective cleaning agent, it is not compatible with a variety of detergent ingredients and may require lengthy soaking time in which the bleach and the stained substrate must remain in contact to ensure stain removal.
Another known bleaching source is diacyl peroxides (DAPs). Although DAPs have been disclosed for use in the laundry and anti-acne area, they have had limited success in liquid or automatic dishwashing detergent area. In the laundry field certain diacyl peroxides have been disclosed as beneficial in cleaning tea stains from fibrous material. It has now been discovered that DAPs can improve stain removal performance on plastics.
Another problem facing formulators is stability of the bleaching agents and other individual ingredients over time, especially in liquid products. This is particularly true for diacyl peroxides in alkaline conditions.
As a consequence to the above-identified problems, there has been a substantial amount of research to develop bleaching systems which are stable and effective in liquid formulations and in which the amount of soaking time needed to remove stains is greatly reduced. By the present invention, it has now been discovered that certain bleaching agents are stable and perform very well on stains when the bleaching agent is applied to a substrate and subjected to microwaves. Accordingly, the present invention solves the long-standing need for an inexpensive bleaching system which performs efficiently and effectively under mixed soil load conditions, especially mixtures of hydrophobic and hydrophilic soils.
The detergent compositions provided herein have the property of removing stains, especially tea, fruit juice and carotenoid stains objected to by the consumer from plastic dishware, glass, wood, and many other known substrates when exposed to microwaving from any typical household or commercial microwave. The compositions have other cleaning benefits in addition to stain removal advantages such as deodorizing and disinfecting. Thus, provided herein is a method of removing stains from a substrate by applying a bleaching compositions and exposing the stained substrate to microwaves to provide powerful cleaning of wide-ranging stains while retaining the advantages of a stable, mild product matrix.